The shell gland of the laying hen is one of the most active calcium-depositing tissues. Little is known, however, about the mechanism of calcium transport in this or other mineralizing tissues, such as bone and teeth. The objective of the proposed research is to develop the biochemical tools needed for an investigation of shell gland calcium transport in membrane vesicles in vitro. The ultimate goal of these studies is to determine the biochemical mechanism of transepithelial calcium transport in calcium-depositing tissues. The proposed research will proceed in four stages: 1. The establishment of plasma membrane markers through the use of cell surface-specific labelling reagents; 2. the development of a subcellular fractionation method for shell gland which resolves the various plasma membrane segments (brush border and basal-lateral); 3. the investigation of the role of a calcium and magnesium-dependent ATPase in shell gland calcium transport; and 4. the investigation of the permeability of shell gland brush border membrane vesicles to calcium. The completion of these objectives is necessary to allow the quantitative study of the kinetic and bioenergetic properties of the shell gland calcium transport system, and the eventual resolution of the biochemical mechanism of calcium transport in this tissue. The results of these studies are also relevant to the mechanism of hormonal regulation of calcium transport in the shell gland and other mineralizing tissues.